Method of making an inflatable core



NOV. 22, T HUNTER METHOD OF MAKING AN INFLATABLE CORE Original Filed Aug. 9, 1950 2 Sheets-Sheet 1 7 000 000 0 O V .24 v 3 v Jarneys Nov. 22, 1955 E. T. HUNTER METHOD OF MAKING AN INFLATABLE CORE 2 Sheets-Sheet 2 Original Filed Aug. 9, 1950 IL m RN mN hN United States Patent METHOD OF MAKING AN INFLATABLE CORE Eldred Tait Hunter, Kingston, Jamaica, British West Indies Originalapplication August 9, 1950, Serial No. 178,536,

new Patent No. 2,685,118, dated August 3, 1954. Di-

vided and this application April 24, 1953, Serial No. 350,945

Claims priority, application Great Britain August 16, 1949 13 Claims. (Cl. 154-83) This invention relates to the method of making an inflatable core and the present application constitutes a division of my co-pending application Serial No. 178,53 6, filed August 9, 1950, now Patent No. 2,635,113, and originally entitled Inflatable Cores and Method of Making Same.

tained Within the mass in an inflated condition until the mass has hardened and set, following which the core is deflated and removed thereby leaving a substantially smooth surfaced bore in a hardened set mass of concrete or the like, as previously set forth.

It is a primary object of the present invention to provide arnethod of making an inflatable rubber core having such characteristics that it is limited as to the amount of inflation and one that will inflate evenly throughout substantially its entire length.

It is an additional object to provide such a core that on deflation will not adhere to the concrete or such other mass Within which it is embedded and can therefore be readily removed from the set mass.

It is a further object to provide a method of making "an inflatable core that is economical from a standpoint of productive costs and in which the resulting core has 'such characteristics that the size of the finished opening formed in the set masscan be controlled and preselected.

It is an additional object to provide a method of making an inflatable rubber core in long lengths and relative small diameters, these diameters generally not exceeding fourinches after inflation.

While inflatable cores perse are known, the prior art devices cannot be produced in long lengths and small diameters.

The accompanying drawings show several examples embodying the features of the present invention wherein:

Figure 1 is a longitudinal view of the mandrel used in making the rubber core with the original layer of rubber applied thereto,

Figure 2 is a cross section of Figure 1 taken on line 2-4 of Figure l,

Figure 3 is a longitudinal view of the mandrel with the inner rubber shown in Figure l and the core braid applied thereto,

Figure 4 is a cross-sectional view taken on line 4--4 of Figure 3,

Figure 5 is a longitudinal view of the mandrel, the original rubber, the braid and the outer rubbercoating applied thereto,

Figure 6 is a sectional view taken on the line 6--6 of Figure 5,.

Figure 7 is a longitudinal view of the finished core showing the. angle of application of the outer layer of rubber, t

Figure 8 is a diagrammatic view partly broken away to 2,724,673 Patented Nov. 22, 1955 disclose the various layers of the core as made and legend to indicate the tensioning of the braided cord sheath and the canvas wrapper applied to tension the outer rubber layer during the making of the core, and

Figure 9 illustrates a core provided with a plug at one end and an inflatable plug at the other.

With particular reference to Figure 1, a mandrel 1 of the length of the finished core is coated with a rubber layer 2 having the desired thickness. The mandrel is conventional and is approximately fifty feet long in order to fit within the known cooking ovens utilized in curing conventional rubber hoses. The thickness of the layer 2 will vary in accordance with the diameter of core to be produced and the air pressure that must be withstood in inflating the same. Preferably, I utilize practically pure gum rubber in order to obviate any tendency of the rubber to set, which setting would prevent the rubber of a finished core from returning to its original outside diameter after inflation to a greater diameter. Over this layer 2, which in effect constitutes a gum rubber tube and while the same is still in an uncured or tacky state, is braided an expansible and contractable cord sheath 3 illustrated in Figures 34 to 6 and 8. The cords of this sheath are made up of a number of cotton strands having minimum stretch characteristics and a low moisture content and which strands are twisted together. The number and size of the strands in the cords of the braided sheaths vary in accordance with the outside diameter of the finished non-inflated core. For larger core sizes the number of strands and their size are increased. The strands of the cord sheath, which are illustrated diagrammatically in the drawings, are closely laid on to the rubber layer so as to substantially cover the same. The resulting interstices between the strands are very small so that when the core is inflated as hereinafter described and the strands of the sheaths are displaced from their original position relative to the axis of the core the rubber layer 2 is still substantially covered by the sheath. After the cord sheath has been applied a layer of rubber cement of suflicient thickness to wet the sheath and to fill the interstices between the cords is applied and then there is applied an outer rubber sheath 4, as shown in Figures 5 and 6. This outer rubber sheath is of greater thickness than the initial rubber layer 2 and the rubber utilized in this layer has the same characteristic as to purity as the first-mentioned layer. Preferably the outer rubber sheath is applied as a continuous strip spiral wound, as shown in Figure 7. The strip is applied in an uncured or tacky state. The outer rubber sheath can be applied as an envelope, that is, a strip having such width that it can envelope the mandrel, the layer 2 and the sheath and have the end edges abutto provide what amounts to a longitudinal seam running throughout the length of the core. After the outer sheath of rubber is applied a canvas wrapping 5 or wrappings is applied over the previously mentioned layers. This canvas wrapping can constitute one or more layers in the form of an envelope and an outer layer that is spirally wound thereabout under tension. By applying this outer canvas layer in a spiral wound manner or when only a spiral wound layer of canvas wrapping is utilized the ap plication of tension in the winding of the wrapping at an angle to the axis of the core imparts a twist characteristic to the outerrubber layer and which twist characteristic remains when the rubber is cured. After the canvas wrapping has been applied, as indicated in Figure 8, the core length is substantially immediately placed in asu-itable oven and heat treated to cure or set the rubber layers. This is a conventional curing operation except as to, the time element between wrapping and curing and one genorally utilizing steam.

After the core has been cured the canvas wrapping is removed and the mandrel is removed, preferably with the aid of air pressure.

The foregoing steps have produced a fifty foot length of tubing having characteristics described hereinafter. This tubing can produce a core of fifty foot lengths or the tubing can be cut to provide cores of shorter lengths or connected together to provide cores of longer lengths. To complete the manufacture of a core a suitable solid plug or closure 7 is inserted in one end of the desired length of tubing. and metal rings or clamps 8 are tightly applied to the outside of the outer sheath to secure this solid plug in position. The joint must be sufliciently tight to retain the plug in place under the action of air pressure up to 150 pounds per square inch. The other end of the core length receives in a similar manner a tubular plug 10 provided externally with a conventional Schrader tire valve. As shown in Figure 9, rings or clamps 11 are tightly applied to the outer sheath 4 to secure the tubular plug in position. There is thus produced an inflatable core of the desired length. It is to be further noted that the solid plug 7 protrudes from the end of the core a length suflicient to receive a transverse bore 9 for receiving a fish line or leader so that as the core is removed an electrical wire or other conduit can be connected to the plug and drawn into the tube or duct produced by utilizing the inflatable core.

, The braid is applied directly on the inner rubber layer 2 while the same is still wet or tacky and in order to enable an even expansion of the finished core upon inflation it is desirable that the angle between each strand of braid and a line on the surface of and parallel to the axis of the core when inflated should preferably be between 42 and 53. In order to obtain such an angle of the braid it has been found desirable to apply the braid onto the inner rubber layer 2 so that it makes an angle of between 13 and 19 with the axis of the unexpanded core in the case of mandrel diameters between Va and and from 17% to /2 for larger mandrel diameters of theorder of 1%".

The inner rubber and braid will tend to free itself from the surrounding rubber of the outer sheath 4 and hence during inflation of the finished core the braid will limit the expansion and provide an even expansion over the length of the core, the braid changing its angle from that at which it was braided, e. g. about l3-l9 to an angle of '42" to 53 when the core is expanded.

When the fluid in the core is brought under pressure, less than 150 lbs. per square inch, usually in the neighborhood of 40 to 70 lbs. per square inch, the core will shorten in length and increase in diameter. This is then surrounded by wet concrete and on deflation after the concrete has hardened the core will increase in length and decrease in diameter and will come free of the concrete allowing the core to be removed to leave the desired duct. The change in angle of the braid during deflation of the core will cause the latter to contract and lengthen during deflation thus assisting in freeing it from the surrounding concrete.

The outer coating is applied over the treated cord in a continuous strip wound spirally thereon. This is held in place during the first heat treatment and the subsequent steam curing by means of canvas wrapping applied to the surface thereof, so as to obtain a uniform product of the desired outside diameter.

The core made by the above process will have an inner wall'thickness varying from /2 inch to inch depending on the outside diameter of the finished core. The above thicknesses are given for a finished core of inch to 2 inches, which may be inflated to 1 inch to 4 inches.

One sizeis made on a mandrel of an inch in diameter upon which is applied the inner rubber layer ,4; of an inch thick. On this is braided the cord treated with rubber cement and then an external layer of rubber is applied thereon which is approximately A1 of an inch thick. The outside diameter of the finished core is 1% inch and may be expanded to approximately 2 inches, using an internal fluid pressure of 40 to lbs. This will vary depending upon the age of the product, the heavier pressure being necessary with newly made cores. The core is loosened within its surrounding rubber to give a free working restricting sheath surrounding the inner rubber tubing.

This process of using a long mandrel up to'50 feet on which is coated a pure rubber layer and then braiding directly on to the uncured rubber a cord sheath, treating the cord sheath with a rubber cement and applying to this the outer layer of rubber in a tacky condition has led to the production of a satisfactory product where many others have failed. Cores of this type may be made with any outside diameter, which in inflation will range from 1 inch to four inches.

These cores are strong, will stand the rough treatment to which they are subjected, are air tight, may be readily inflated by either a hand pump or compressed air tank and upon deflation will not cling to the cement walls of the conduit formed, and will increase in length so as to be readily removed from the finished conduit.

In connection with the finished core the spiral winding of the canvas wrapping 5 is such that tension is applied to the wrapping as it is being wound on the outer layer 4 and this tension as indicated previously imparts a twist characteristic to the rubber even though it is unset and upon subsequent curing this twist is retained in the rubber. This twist characteristic is important since when the core is inflated it will expand in outside diameter and contract in length. Therefore when the core is deflated the rubber in contracting in diameter and length will twist to restore itself to its original condition and this twist action in deflating will definitely improve the ease of removal of the core from the surrounding concrete or other plastic mass. In other words, every particle of rubber of the outer sheath has moved when the core is deflated and in effect physically tears itself away from any adherence to the inner surface of the duct or tube made in the concrete or like material.

The canvas wrapping is approximately 3" wide and the twist is imparted to the rubber by applying greater tension to one marginal edge of the wrapping as it is being applied. In other words, as the spiral wrapping is laid on the outer rubber sheath one side is pressed toward the rubber under greater tension than the other side of the strip, see Figure 8. Thus in a finished tube or core slight spiral ridges are formed in the outer surface of the outer sheath and alternate edges of the ridges are more pronounced.

In connection with the braiding of the fabric core or sheath on to the inner rubber layer by applying slightly greater tension to some of the cords being braided from one side of the axis of the tube and by braiding uniformly a twisting movement is produced over the whole length of the tube which enhances the twist characteristic applied to the finished core as shown in Figure 8.

It is to be noted that the spiral wrapping 5 is applied at an angle in the same direction as the braid tension. Thus it follows that the braiding imparts a twist to the inner rubber layer which constitutes an expansible and contractable tube which twist is assisted by the twist imparted to the outer rubber layer, also an expansible and contractible tube by the tensioning of the canvas wrapping 5.

Thus it follows that when using my inflatable cores and they are inflated to the size required utilizing 50 to of the tube decreases uniformly by about 15 per cent and since, as previously mentioned, one or more cords of one set of the diagonal cords of the fabric sheath is The tension applied to the tensioned cords is of the order of afew ounces, preferably one to three ounces, greater than the tension in the other cords. This action thereforeiinparts three distinct movements which breaks any key or seal between concrete and the tube must: when the tubeis deflated. First, the decrease in diameter; second, the increase in length, and finally, the twist of the core.

As previously indicated longer runs of inflatable core can be produced by joining two lengths together. Such a joint embodies a placing of the plug ends in abutting relation and a sleeve or length of tubing of the required duct internal diameter is deposited about the abutting ends. Of course, in such an arrangement it is necessary to inflate each length separately but the increased length of tubing is still highly desirable in some installations.

With this type joint upon inflation of the two cores the expansion of the diameter thereof adjacent the plugged end produces a friction fit between the two adjacent core ends and the sleeve surrounding the same to the extent that this joint can only be broken by deflating the respective cores.

If larger ducts are required in concrete than can be obtained from a single core the increased diameter can be obtained by tying tubes or cores together and using them as a unit. For example, a duct approximately 9" by 6" in size can be obtained by using six 3" expanded O. D. cores tied together as a unit. By tying together I mean placing several cores side by side and by, for example, the use of rubber bands holding them in assembled relationship. Alternatively several cores can be inflated, placed in parallelism and tied together by wire, then placed in position and covered with concrete or the like. Upon deflation the individual cores reduce in diameter and can be individually withdrawn and the wire stay embodied in the concrete.

It is further notedthat while the mandrel length is stated to be approximately 50 feet long, there is of course no limitation to the length of the mandrel other than the length of the cooking oven utilized to cure the rubber; for example, in European practice the ovens are approximately 60 feet long thus necessitating the use of a 60 foot mandrel in carrying out the process. If larger ovens are available, the mandrel can be lengthened accordingly.

What I claim is:

1. In a method of manufacturing inflatable cores for use in making tubular openings in cementitious masses, the steps of applying a layer of uncured rubber to a mandrel, applying a contractable sheath of strands around said layer while imparting a twist characteristic thereto, applying an outer layer of uncured rubber over said sheath and exerting a twisting force upon said outer layer to impart a similar twist characteristic to said outer layer.

2. A method as defined in and by claim 1, in which the outer rubber layer is applied in a tacky condition.

3. A method as defined in and by claim 1 in which the outer rubber layer isapplied in the form of a continuous spirally wound strip.

4. A method. as defined in and by claim 1 in which said sheath constitutes braided cord and in which the cord is closely braided about the first-mentioned rubber layer while the same is in an uncured state while applying greater tension to some of the cords braided from one side of the longitudinal axis of the mandrel than is applied to the other cords braided from the same side to impart a twist characteristic to said inner rubber layer.

5. A method as defined in and by claim 4 in which a layer of rubber cement suflicient to wet the cords and said sheath and to fill the interstices between the cords is. applied to the sheath prior to applying the outer. rubber layer.

6. In a method of manufacturing inflatable rubber cores; the steps of applying a layerof uncured rubber to a mandrel, braiding a sheath of cords about said layer while the same is in an uncured state with the cords extending at an angle of between 13 and 25% with respect to the axis of the mandrel while applying greater tension to at least some of the cords being braided from one side of the axis of the mandrel. than is applied to the others braided from the same side, applying an outer rubber sheath over said braided sheath and curing the rubber while imparting tension to said outer rubber sheath in the same direction as the greater tension applied to some of the cords so as to impart a similar twist characteristic to the outer rubber sheath.

7. A method of manufacturing inflatable rubber cores including applying a layer of uncured rubber to a mandrel, uniformly braiding a sheath of cords about said layer while the same is in an uncured state, the cords of the sheath being disposed at an angle of between 13 and 25 /2" with respect to the axis of the mandrel, and applying greater tension to at least some of the cords being braided from one side of the axis of the mandrel than is applied to the others braided from the same side, applying an outer rubber sheath over said first-mentioned sheath, spirally winding a fabric strip wrapping over said outer rubber sheath while applying greater tension along one marginal edge of the strip, the tension applied to the wrapping being in the same direction as the greater tension applied to the cords, curing the rubber, removing the wrapping and removing the mandrel.

8. A method as defined in and by claim 7 in which the outer rubber sheath is of greater thickness than the first-mentioned layer of rubber and in which a layer of rubber cement suflicient to wet said braided sheath is applied thereto prior to applying the outer rubber sheath.

9. In a method of producing elongated comparatively small diameter inflatable cores of the type that are plugged at one end and valved at the other the steps of applying an expansible and contractable sheath of diagonally arranged cords about an uncured gum rubber tube while applying greater tension to some of the cords extending from one side of the longitudinal axis of the tube than to the others extending from the same side to provide for twisting movement in one direction, applying an uncured rubber sheath about said first-mentioned sheath and curing the rubber while exerting a twisting force upon said outer rubber sheath to impart a twist characteristic thereto similar to the twist imparted to the cord sheath by the greater tensioning applied to some of the cords.

10. A method as defined in and by claim 9 in which before curing the outer rubber sheath is wrapped with a fabric strip at an angle and under tension applied in the same direction as the greater tension applied to some of the cords of the first-mentioned sheath while applying greater tension along one marginal edge of the strip to exert a twisting force upon said outer rubber sheath and to impart the twist characteristic thereto.

11. A method as defined in and by claim 10 and in which after curing, the strip wrapping is removed and fixedly securing a plug in one end of the cured composite tube and a valve in the other.

12. In a method of producing inflatable cores of the type used in concrete construction which are plugged at one end and have a valve at the other, the steps of applying an expansible and contractable sheath of tensioned cords about an expansible and contractable tube while applying greater tension to some of the cores applied from one side of the longitudinal axis of the tube than is applied to other cords applied from the same side to impart a twist characteristic to said sheath and thus to said tube, applying an expansible and contractable rubber cover about said sheath and tensioning said cover in the same direction as the greater tension applied to 'someof the said cords to impart a similar twist characteristic to said cover. I

13. A method as defined in by claim 12 and plugging References Cited in the file of this patent UNITED STATES PATENTS Subers Dec. 5, 1911 1 Cobb June 26, 1917 Austin Aug. 7, 1928 Pahl June 20, 1933 Lindas Mar. 6, 1934 Price Mar. 2, 1943 

1. IN A METHOD OF MANUFACTURING INFLATABLE CORES FOR USE IN MAKING TUBULAR OPENINGS IN CEMENTITIOUS MASSES, THE STEPS OF APPLYING A LAYER OF UNCURED RUBBER TO A MANDREL, APPLYING A CONTRACTABLE SHEATH OF STRANDS AROUND SAID LAYER WHILE IMPARTING A TWIST CHARACTERISTIC THERETO, APPLYING AN OUTER LAYER OF UNCURED RUBBER OVER SAID SHEATH AND EXERTING A TWISTING FORCE UPON SAID OUTER 